1. Field of the Invention
This invention relates generally to chemical mechanical planarization apparatuses, and more particularly to methods and apparatuses for improved uniformity in chemical mechanical planarization applications via controlling temperature of a polishing pad.
2. Description of the Related Art
In the fabrication of semiconductor devices, there is a need to perform chemical mechanical planarization (CMP) operations. Typically, integrated circuit devices are in the form of multi-level structures. At the substrate level, transistor devices having diffusion zones are formed. In subsequent levels, interconnect metallization lines are patterned and electrically connected to the transistor devices to define the desired functional device. As is well known, patterned conductive layers are insulated from other conductive layers by dielectric materials, such as silicon dioxide. As more metallization levels and associated dielectric layers are formed, the need to planarize the dielectric material grows. Without planarization, fabrication of further metallization layers becomes substantially more difficult due to the variations in the surface topography. In other applications, metallization line patterns are formed in the dielectric material, and then, metal CMP operations are performed to remove excess material.
A chemical mechanical planarization (CMP) system is typically utilized to polish a wafer as described above. A CMP system typically includes system components for handling and polishing the surface of a wafer. Such components can be, for example, an orbital polishing pad, or a linear belt polishing pad. The pad itself is typically made of a polyurethane material or polyurethane in conjunction with other materials such as, for example a stainless steel belt. In operation, the belt pad is put in motion and then a slurry material is applied and spread over the surface of the belt pad. Once the belt pad having slurry on it is moving at a desired rate, the wafer is lowered onto the surface of the belt pad. In this manner, wafer surface that is desired to be planarized is substantially smoothed, much like sandpaper may be used to sand wood. The wafer may then be cleaned in a wafer cleaning system.
FIG. 1A shows a linear polishing apparatus 10 which is typically utilized in a CMP system. The linear polishing apparatus 10 polishes away materials on a surface of a semiconductor wafer 16. The material being removed may be a substrate material of the wafer 16 or one or more layers formed on the wafer 16. Such a layer typically includes one or more of any type of material formed or present during a CMP process such as, for example, dielectric materials, silicon nitride, metals (e.g., aluminum and copper), metal alloys, semiconductor materials, etc. Typically, CMP may be utilized to polish the one or more of the layers on the wafer 16 to planarize a surface layer of the wafer 16.
The linear polishing apparatus 10 utilizes a polishing belt 12, which moves linearly in respect to the surface of the wafer 16. The belt 12 is a continuous belt rotating about rollers (or spindles) 20. A motor typically drives the rollers so that the rotational motion of the rollers 20 causes the polishing belt 12 to be driven in a linear motion 22 with respect to the wafer 16.
A wafer carrier 18 holds the wafer 16. The wafer 16 is typically held in position by mechanical retaining ring and/or by vacuum. The wafer carrier positions the wafer atop the polishing belt 12 so that the surface of the wafer 16 comes in contact with a polishing surface of the polishing belt 12.
FIG. 1B shows a side view of the linear polishing apparatus 10. As discussed above in reference to FIG. 1A, the wafer carrier 18 holds the wafer 16 in position over the polishing belt 12 while applying pressure to the polishing belt. The polishing belt 12 is a continuous belt typically made up of a polymer material such as, for example, the IC 1000 made by Rodel, Inc. layered upon a supporting layer. The polishing belt 12 is rotated by the rollers 20 which drives the polishing belt in the linear motion 22 with respect to the wafer 16. In one example, a fluid bearing platen 24 supports a section of the polishing belt under the zone where the wafer 16 is applied. The platen 24 can then be used to apply fluid against the under surface of the supporting layer. The applied fluid thus forms a fluid bearing that creates a polishing pressure on the underside of the polishing belt 12 which is applied against the surface of the wafer 16. Unfortunately, because the polishing rate produced by the fluid bearing typically cannot be controlled very well, the polishing pressure applied by the fluid bearing is non-uniform. Specifically, the temperature of the polishing belt 12 often varies during the polishing process. The polishing belt 12 typically starts off cold and becomes warmer during the wafer polishing. As wafer polishing progresses, the temperature of the polishing belt increases due to the friction between the polishing belt 12, the slurry, and the wafer 16. This is extremely problematic because as the temperature of the polishing belt 12 increases, this increases the temperature of the slurry used in the polishing process which then increases the polishing rate of the wafer 16. In addition, when air is used as the fluid bearing, the air released from the platen 24 is generally extremely cold. This occurs because as the air is outputted from the air output holes in the platen 24, air expands and therefore becomes colder. Therefore, due to the frictional heat and the cold air from the platen 24, it is generally very difficult to control the polishing belt temperature. As a result, due to the fact that the prior art polishing system designs do not properly control polishing dynamics, uneven polishing and inconsistent wafer polishing may result thereby decreasing wafer yield and increasing wafer costs.
In view of the foregoing, there is a need for an apparatus that overcomes the problems of the prior art by having a platen that improves polishing pad temperature control and reduces polishing rate discrepancies.